There has been an extraordinary expansion in the interest in being able to measure a wide variety of analytes. This interest has been not only in the field of medicine, but also in other fields, such as processing, molecular biology, ecology and the like. The field of diagnostics has seen the evolution of techniques in whole or in part in solution, involving separation steps or eschewing separation steps, where each of the methods have evolved to provide techniques allowing for detection of analytes at ng/ml levels. However, the solution techniques involve, for the most part, careful measurements, sophisticated instrumentation, and technical sophistication. These techniques have therefore found their primary use in laboratories, which have the available equipment and expertise to perform the assays.
In conjunction with the development of the solution assays, there has been an extensive effort to produce assays involving devices which do not require technical skill. These devices have been primarily directed to the use of sticks or capillaries where the device is contacted with the sample and most of the chemistry is carried out on the device. Usually, the technique requires relatively simple measurements of the sample and/or reagents, and the result can be read either visually or by relatively simple instrumentation. For the most part, these results do not involve a need for accurate quantitative determinations where the amount of analyte is present at extraordinary low concentrations.
Nevertheless, there is an increasing need in hospitals, doctors' offices and in the home to be able to detect a wide variety of analytes which are present at low concentrations, where an accurate determination is necessary for the information to be useful. There still remains a need to provide techniques with simple protocols which can be measured by relatively unsophisticated instrumentation.